Photo-generated high-energy surface states can help to produce chlorine in aqueous environments. Here, aligned rutile (TiO2) nanocrystal arrays are grown onto fluorine-doped tin oxide (FTO) substrates and activated either by hydrothermal Sr/Ba surface doping and/or by vacuum-annealing. With vacuum-annealing, highly photo-active films are obtained with photocurrents of typically 8 mA cm-2 at 1.0 V vs. SCE in 1 M KCl (LED illumination with  = 385 nm and approx. 100 mW cm-2). Photoelectrochemical chlorine production is demonstrated in proof-of-concept scale in 4 M NaCl and suggested to be linked mainly to the production of Ti(III) surface species by vacuum-annealing, as detected by XPS, rather than to Sr/Ba doping at the rutile surface. The vacuum-annealing treatment is proposed to beneficially affect (i) bulk semiconductor TiO2 nanocrystal properties and electron harvesting, (ii) surface TiO2 reactivity towards chloride adsorption and oxidation, and (iii) FTO substrate performance.
Original languageEnglish
Pages (from-to)65-77
Number of pages13
Early online date9 Nov 2020
Publication statusPublished - 31 Jan 2021


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